Rapid tannage of sole leather



United States Patent 3,027,221 RAPID TANNAGE 0F SBLE LEATHER Clarence W. Beebe, Roslyn, Muriel L. Happich, Jenkintown, Joseph Naghski, Philadelphia, and Wallace Windus, Meadowbi'ook, Pa., assignors to the United States of America as represented by the Secretary of Agriculture No Drawing. Filed Sept. 16, 1959, Ser. No. 840,477

3 Claims. (Cl. 8--94.33) (Granted under Title 35, US. Code (1952), see. 256) A non-exclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is hereby granted to the Government of the United States of America.

This invention relates to rapid tannage of heavy hides in the production of sole leather. More particularly, this invention relates to a vegetable tannage in which only strong vegetable tannin extracts are employed.

Sole leather is usually made from cattle hides tanned with vegetable tannins, such as those obtained from chestnut or quebracho wood or wattle bark. The current tannage of such leather is a relatively long process, usually lasting for at least 6 Weeks. The hide is put into a liquor of low tannin content, such as 0.5 to 1.0% tannin, and the liquor is gradually strengthened. Attempts to accelerate the tannage by the use of stronger liquors is not practical because of the danger of case-hardening where the outside layers of the hide are overtanned, while the center is still raw. If the tan liquors are heavily sulfited to increase their penetration into the hide, combination of the tannins with the hide is poor and the result is a low yield of fiat leather. The use of mechanical motion, such as a drum or a paddle, has been used to accelerate penetration of vegetable tannin into the hide, but this causes excessive damage to the leather unless the hide is quite well tanned before drumming.

Several rapid tanning procedures for making sole leather have been proposed, but none give leather having the desirable qualities obtained by conventional vegetable tanning. For example, if a hide is tanned with form aldehyde it may be retanned with vegetable tannin quite rapidly, but the leather is flat and tinny with a cracky grain and cannot be properly channeled and sewn. Chrome tannage followed by vegetable tannage gives a leather of loose structure. This leather is too flexible for good sole leather and requires filling with wax or other materials. Other rapid tannages use no vegetable tannin in the process and give leathers which find only limited use in the trade.

An object of this invention is to provide a rapid process for tanning sole leather. Another object of this inventoin is to provide a rapid vegetable tanning process. A further object is to vegetable tan sole leather employing only strong tan liquors. Still another object is to provide a tanning process in which the vegetable tanning liquors may be used indefinitely. Other objects will become apparent upon examination of the examples and claims.

We have found that a pretannage of heavy hides with dialdehyde starch permits immediate tannage with strong vegetable tan liquor without the usual attendant difficulties and produces a sole leather with substantially all the desirable properties of leather obtained by the conventional vegetable tanning process.

According to the present invention heavy hides are delimed, subjected to the action of an aqueous dialdehyde starch solution, preferably a solution containing an amount of dialdehyde starch representing about to by weight of the white hide, at a pH in the range of about 7.5 to 8.5, preferably about pH 8.0, until dialdehyde starch has penetrated to and reacted with the center of 3,il27,22l

Patented Mar. 27, 1952 the hide, giving a pretanned hide, the pretanned hide washed with water and impregnated with a solution containing about 10 to 15% (weight/volume) of vegetable tannins at a pH of about 4 until the hides are tanned.

By heavy hides we mean those hides or portions of hides that are conventionally used for the preparation of leather for use as shoe soles. Hide white weight is the weight of a wet unhaired, limed hide ready for starting through the tanning process.

Although dialdehyde starch tannage of light-weight skins such as sheepskin, goatskin, calfskin, and certain sections or layers of cowhide produces excellent leather, when applied to heavy hides the product is spongy and is not satisfactory for use as sole leather. Hence, while dialdehyde starch reacts with the heavy hide, in the absence of a useful leather from this operation, it has been designated in the present process as a pretannage.

The pretannage with dialdehyde starch conditions the heavy hide so that it may be tanned rapidly with strong vegetable tanning liquors. As demonstrated in the examples to follow, the vegetable tannage may be performed in either vat or drum. Whereas delimed hides still contain calcium salts which react with vegetable tanning liquors, forming precipitates and decreasing the activity of the liquor, the treatment with dialdehyde starch appears to inactivate the calcium, perhaps by binding or chelating action. Hence, the tanning activity of the liquor is more effective and the liquors last longer.

The final product of the present invention, obtained in about one week, is primarily a well-filled vegetable tanned leather with substantially the yield and chemical analysis of leather obtained in about six weeks by the conventional vegetable tannage. The leather is usually somewhat lighter in color than regular vegetable tanned sole leather and tends to be slightly more mellow, properties desired in the trade.

Satisfactory dialdehyde starch pretannage was achieved with heavy hides which had been delimed at either pH 4.8 to 5.2 or at pH 7.8 to 8.5. It is important that the hide be placed in a proper state of plumpness prior to the dialdehyde starch pretannage and that the dialdehyde starch pretannage be carried out under conditions which will preserve the proper state for tanning with vegetable tans. The desirable condition for the dialdehyde starch pretannage is limited to a pH range of about 7.5 to 8.5, preferably about pH 8. The pretanned bide going into the strong vegetable tanning liquors should not be too flaccid, which will lead to drawn grain, or too swollen, which will lead to poor penetration of the vegetable tannins or even to case-hardening.

The time factor involved in the pretannage with dialdehyde starch will vary somewhat with thickness of hide, movement of hide in solution, etc. Satisfactory conditioning of heavy hides has been achieved in about one day, but a two-day treatment is considered preferable to insure reaction of dialdehyde starch with the innermost regions of the hide. The dialdehyde starch was a typical commercial product in which or more of the anhydroglucose units had been converted to the aldehyde structure.

The dialdehyde starch solution from a pretannage may be reused for five or more times, as described in Example VII, by adding more dialdehyde starch and, if necessary, adjusting the volume and pH of the aqueous solution.

After the dialdehyde starch pretannage the hides are preferably washed in water. This removes excess salts and dialdehyde starch which would otherwise contaminate the vegetable tanning liquor and which might interfere with uniform tannage of the hide.

A very important feature of this process is that the vegetable tanning liquors may be used indefinitely by a) drawing off about of the volume after each run to make room for adding fresh tanning extract. While somewhat lower or higher concentrations of tannin may be used, we prefer a tan liquor containing about 10 to (weight/volume basis) of the vegetable tannins conventionally employed for tanning sole leather, such as a blend of about equal parts of chestnut extract and sulfited quebracho extract or other blends having similar tanning properties. The pH should be about 4 for the vegetable tannage of sole leather.

The process of the present invention is further illustrated by the following examples.

EXAMPLE I One side of cowhide was soaked in the usual manner, the hair loosened with lime-sulfide solution, unhaired, washed and then immersed for 18 hours in a deliming solution containing 2% ammonium chloride and 0.1% commerical bate (based on the hide white weight) for partial or complete deliming. The pH of a freshly cut cross-section of the clelimed hide was approximately 8.0 as determined by phenolphthalein. The side was Washed approximately one-half hour in running water, then attached to a frame and suspended in a vat of aqueous dialdehyde starch solution for pretannage. The dialdehyde starch solution contained 5% dialdehyde starch, 6.3% sodium bicarbonate (both materials based on the hide white weight), 8% sodium sulfate (on the solution basis) and had a pH of 7.9. The liquor to hide ratio was 5:1. After 48 hours in this solution the pretanned side had a shrinkage temperature of about 76 C., and the pretannage was considered sufficient for tannage with vegetable extract. After washing for an hour in a vat of water to remove salts and free dialdehyde starch the pretanned side was immersed in a vat of vegetable extract contain ing 14% tannin made up of approximately 50% clarified quebracho and 50% foreign chestnut extract on the tannin basis. The pH at the beginning of the vegetable tannage was 4.12 and the liquor to hide ratio was 5:1. The pretanned hide was completely penetrated with the vegetable extract in 5 days without any motion. The leather was next washed, oiled lightly, dried and sent to a commercial tannery for finishing as sole leather. On analysis this leather had a degree of tannage of 6.6.0 and a gain (white Weight to finish weight) of 72.0%.

EXAMPLE II The. process of Example I was repeated on another side of cowhide using exactly the same conditions except for using 10% dialdehyde starch in the pretanning solution and float ratios of 4.5 to 1.

On analysis the finished sole leather had a degree of tannage of 66.8 and a gain (white weight to finish weight) of 73.1%.

EXAMPLE III An unhaired, washed side Was delimed by immersing for 48 hours in a solution containing 10% sodium chloride, 3.5 sodium acetate and 1.8% glacial acetic acid, using a solution to hide ratio of 5: 1. After this time interval the pH of the solution was 4.8 and that of the hide 4.8 to 5.0 (near the isoelectric point of the hide). The side was washed; then pretanned (10% dialdehyde starch and pH 8.0) and tanned (14% tannin) as in Example IE. Part of the tanned side was finished as sole leather in a commercial tannery and resulted in an excellent product essentially like that of Examples I and II.

EXAMPLE V A side of cowhide was soaked, unhaired after treatment with lime-sulfide solution, washed, and immersed for about 65 hours (over the weekend) in a buffer solution (3:1 solution-to-hide ratio) containing 10% sodium chloride, 5% sodium acetate, and 2.5% glacial acetic acid. The side (pH 4.75.0) was washed, hung in a frame and immersed for 72 hours in a vat of solution containing 15% dialdehyde starch, 6.3% sodium carbonate (both based on weight of white hide) and about 10% sodium sulfate (based on volume of solution) at pH 7.9. The solution to hide ratio was about 7.5 1. After washing the side was placed in a drum with tan liquor containing about 15% tannins (50% clarified quebracho and 50 foreign chestnut) at pH 3.7 and a liquor to hide ratio of 6:1. The side was drummed 4 /2 hours, allowed to stand in the liquor for about 64 hours, then drummed 6 hours, washed, oiled lightly and dried. Upon finishing at a commercial tannery a good yield of sole leather with a degree of tannage of 67 and a good feel and appearance was obtained.

EXAMPLE V One side of a cowhide was soaked in the usual manner, unhaired after treatment with a lime-sulfide solution, washed and then immersed for 24 hours in a butter solution of 10% sodium chloride, 6% sodium acetate and 3.3% glacial acetic acid using a solution to hide ratio of 4:1. The pH of this buffer solution was 4.9. After washing the side was pretanned in a drum in a solution containing 15% dialdehyde starch, 6.3% sodium bicarbonate (both based on the hide white weight) and 10% sodium sulfate (based on the solution). The pH of the solution was 8.1 and the ratio of solution to hide was 3.5:1.

The drum containing the side and dialdehyde starch solution was rotated for 5 to 10 minutes, then let stand for 2 hours, taking care that the side was submerged in the solution. The drum was then rotated for 5 to 10 minutes and let stand overnight with the side submerged. The next morning the drum was rotated for 1020 minutes, then let stand for about 6 hours. The drum was again rotated for 10-20 minutes and let stand overnight. The next morning the drum was rotated for two one-half hour periods. Following this, the pretanned side was washed. The shrinkage temperature after 48 hours in the dialdehyde starch solution was 7778 C.

The pretanned side was put in a tanning drum in a solution of vegetable. extract containing 14% tannin and made up of approximately 50% clarified quebracho and 50% foreign chestnut extract on the tannin basis. The pH of the solution was 3.9 and the liquor to hide ratio was 6:1. The drum with pretanned side and vegetable liquor was rotated for 2 /2 hours and then let stand with the side submerged under the liquor for the weekend. Sixty-four hours later the side was drummed for an 8 hour period, then allowed to stand all night. The next day, it was washed, oiled lightly, dried, and part of it finished into sole leather. The finished leather had a satisfactory appearance. The bends had a degree of tannage of 78.9 and a gain of 72% (white weight to finish weight).

The following examples (VI and VII) illustrate the reuse of strong vegetable tanning liquors and of dialdehyde starch solutions in the process of the present invention.

EXAMPLE VI A side of cowhide was soaked, delirned, washed and pretanned with 5% dialdehyde starch as described in Example I.

The vegetable tanning liquor, originally prepared as in Example I, had been previously used for twenty consecutive tannages. After each tannage about 10% of the volume was withdrawn and suflicient fresh concentrated extract added to the remaining liquor to bring the tannin content to about 14 to 15%. If the pH had changed during a tannage it was adjusted to about pH 4 before starting the next tannage.

The dialdehyde starch pretanned hide was tanned in a vat of this vegetable tanning liquor for 6 days. The tanned hide was washed, oiled lightly, dried, andfinished'.

to the product of Example I.

EXAMELE VII The bend portion of a hide was unhaired after treatment in a lime-sulfide solution. The unhaired bend was Washed and put in a solution of calcium hydroxide until used. As they were needed, duplicate pieces of hide were cut from the bend, delimed in a 2% solution of ammonium chloride and 0.1% commercial bate (based on the hide white weight), washed, and, With a hide pH of about 8.0-8.5 were put into a solution containing 5% dialdehyde starch, 6.3% sodium bicarbonate (based on the hide white weight) and 8% sodium sulfate (based on the solution) in a small vat. The ratio of solution to hide was 5:1 and was kept constant. This solution was used 5 consecutive times pretanning two pieces of hide each time and the volume did not change appreciably. The pH of the solution at the beginning of each of the five dialdehyde starch pretannages ranged from 7.8 to 8.4. Sodium bicarbonate was added when necessary to keep within this range. Four percent dialdehydc starch based on the white weight of the hide entering the liquor was used to restrengthen the dialdehyde starch solution before each reuse. After two days in the dialdehyde starch solution the pretanned hide pieces were considered ready for vegetable tannage. They were then washed and put into a small vat of a fresh solution of vegetable tanning liquor containing 16 to 17% tannin (made up of approximately 50% clarified quebracho extract and 50% foreign chestnut extract on the tannin basis). The pH of each vegetable liquor used was 3.6- 3.7. The liquor to hide ratio was approximately 5:1. The pretanned hide pieces were tanned in the vegetabie extract in 5 to 6 days. Penetration proceeded evenly into the pretanned hide from both the flesh and grain sides. After vegetable tannage the pieces were Washed and dried. The data for this example are summarized in Table 1.

Table I.Dat:t on Reuse of Dialde hyde Starch Solution for 5 Times to P/ etc'n Hide for Subsequent Vegetable Tonnage No. of times dialdehyde starch solution used 1 2 3 4 5 Grams of hide per prctannage 485 520 540 530 575 Grains of dialdehyde starch added. 24. 3 21.0 21. 6 21. 2 22. Grams of NaHCO added 30.6 0 0 10 20 Mls. of 8% Nt2$0 added 2425 O 0 0 0 pH at start of pretannage 8. 43 8. 1t) 7. 80 7. 80 7. 82 pH after 48 hours 8. 28 8. 7. 72 7. 68 7. B8 Shrinkage temperature after 48 76 79 76 75 76 hours of prctannage, C 72 82 77 77 77 Time 01' prctannage, hours. 48 43 48 48 48 Mls. of fresh vegetable liqu used in tannage 2, 200 2, 200 2, 400 2, 400 2, 400 Percent Tannin of liquor. 17.1 17. 2 15. 8 15. 8 15. 7 pH at beginning of taunago 3. 65 3. 63 3. 66 3. 7 3. 72 Time 01' tannage, days 5 5 .5 5 5-6 All 10 pieces of leather were rated as good sole leather on the basis of appearance feel and analyses. The results showed that with strengthening the dialdchyde starch content and adjusting the pH after each run a vat of dialdehyde starch solution may be reused several times. Thus the dialdehyde starch preconditioning of heavy hides may be accomplished with very little waste of dialdehyde starch in spent liquors.

The practical operation or" the present invention is demonstrated in the following example.

XAMPLE VIII Ten heavy native cowhides (2O sides) were soaked in the usual manner unhaired after treatment with a limesulfide solution washed and weighed in a commercial 6 tannery where they were tanned according to the following procedure.

The 10 hides were delimed a solution containing 2% ammonium chloride and 0.1% commercial bate (both based on the hide white weight) in a rocker vat during a 20-hour period. The pH of the hides after delirning was between 8.0 and 8.6. The hides were next Washed in a paddle and then hung in a rocker in a solution of dialdehyde starch containing 5% dialdehyde starch 6.3% sodium bicarbonate (both based on the hide white weight) and 8% sodium sulfate (based on the solution) and having a pH of 7.8. The ratio of hide was 6:1 (600% float). After 44 hours the hides were completely penetrated with the dialdehyde starch solution and the shrinkage temperature of the hide was 78-79 C. The hides were washed in the rocker and then transferred to another rocker containing this tannerys blend of vegetable tanning liquor with a tannin content or" 10% and a pH of 3.8. During the vegetable tannage which required 6 days the vegetable liquor was adjusted back to 10% tannin twice and the pH adjusted to 4.0-4.1 each time. The liquor to hide ratio was 6:1.

The 10 tanned cowhides were finished in the tannery with regular production. The backs were Wheel extracted, tempered 5 days, bleached, wrung, oil wheeled, set out, dried, dipped, rolled, dried, brushed and rolled. The bellies were bleached, wrung, oil wheeled, set out, dried, dipped, rolled and dried. In each instance the white weight yield was 67.8%.

Tannery comments regarding backs: general appearance was good; color slightly lighter than regular leather; temper slightly more mellow than obtained in their usual sole leather tannage; no difficulty encountered in cutting soles; soles could be leveled and degrained satisfactorily; and degree of tannage was 66.6.

Tannery comments regarding bellies: general appearance comparable to regular leather; temper somewhat more mellow; no ditficulty in handling through cutting operations; and degree of tannage was 71.0.

We claim:

1. A process for tanning a heavy hide comprising subjecting a delimed hide to the action of an aqueous dialdehyde starch solution at a pH in the range of about 7.5 to 8.5 until dialdehyde starch has reacted. with the innermost regions of the hide to pretan the hide, Washing the pretanned hide with water, and impregnating the washed, pretanned hide with a solution containing about 10 to 15% of vegeable tannins at a pH of about 4 until the hide is tanned.

2. The process of claim 1 in which the aqueous dialdehyde starch solution contains about 5 to 15 dialdehyde starch, based upon hide white weight.

3. The process of claim 2 in which the dialdehyde starch solution has a pH of about 8.

References Cited in the file of this patent UNITED STATES PATENTS 2,351,338 Howard June 13, 1944 2,851,329 Seligsberger Sept. 9, 1958 2,880,236 Mehltretter ct a l. Mar. 31, 1959 OTHER REFERENCES Utilizati n Research on Hides and Leather Reprint from The Leather Manufacturer, August 1959, 4 pages.

C & E News, Dec. 9, 1957, vol. 35, No. 49; pp. 58-59.

J.A.L.C.A., February 1958, vol. 1.111, No. 2 pp. 77-85.

Progress in Leather Science, 1920-1945, London, 1948, p. 514.

OFlaherty et al.: Chemistry and Technology of Leather, Reinhold Pub. Corp., N.Y., 1958. vol. 2, pp. 189- 190. 

1. A PROCESS FOR TANNING A HEAVY HIDE COMPRISING SUBJECTING A DELIMED HIDE TO THE ACTION OF AN AQUEOUS DIALDEHYDE STARCH SOLUTION AT A PH IN THE RANGE OF ABOUT 7.5 TO 8.5 UNTIL DIALDEHYDE STARCH HAS REACTED WITH THE INNERMOST REGIONS OF THE HIDE TO PRETAN THE HIDE, WASHING THE PRETANNED HIDE WITH WATER, AND IMPREGNATING THE WASHED, PRETANNED HIDE WITH A SOLUTION CONTAINING ABOUT 10 TO 15% OF VEGEABLE TANNINS AT A PH OF ABOUT 4 UNTIL THE HIDE IS TANNED. 